Signors



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R. MERCER ET AL TELEPHONE SYSTEM Filed Sept. 6, 1924 8 Shtseet '7 ImrE'n01'' Richard MEPEEP- Frank T211021 W 5-- Oct. 16, 192E. msmso R. MERCERET AL TELEPHONE SYSTEM Filed Sept.6,'l924 8 Sheets-Sheet 8 1W5? EmhardPIEPEEP Frank Teach Err-g I Patented ea. is, 1928.

warren stares "earner GFFHCE.

RICHARD MERCER, OF HARROW, AND FRANK TENCH, OF LONDON, ENGLAND, AS-

SIGNORS, BY MESNE ASSIGNMENTS, T0 AUTOMATIC ELECTRIC INC, OF CHICAGO,

ILLINOIS, A CORPORATION OF DELAWARE.

TELEPHONE SYSTEM.

Application filed September 6, 1924., Serial No. 736,354; and in GreatBritain September 18, 1923.

' The present invention concerns improvements in or relating toautomatic telephone systems, more particularly systems of the type inwhich the automatic switches are directly controlled by the subscriber.Since the subscribers dial has usually ten finger holes the switching insuch systems will normally be on the decimalprinciple, i. e. the numberof contacts upon which the switches can be set by impulses will be apower of 10. Such a system if used without any modification is apt to beuneconomical in the case of small exchanges of say, from 1000 to 5000lines or in small networks having less than five exchanges since a largeproportion of the first selector bank is unused. Accordingly the objectof the present invention may be stated generally to be the provision ofimproved switches and improved trunking arrangements whereby a moreefiicient utilization of the switches is possible and in the case ofexchanges of from 1000 to 4000 lines capacity a switching stage may beentirely saved. the switches employed are of the type known as largecapacity switches i. e. they have more than one set of wipers and acorresponding number of banks, the particular set to be used beingselected according to requirements.

The feature of the invention broadly stated is the more efficient oreconomic utilization of switches owing to the superior efficiency oflarge groups of trunks which additionaleificiency is attained by meansindividual to the switches and independently of any increase in thenumber of leads between the switches of one stage and the switches of apreceding stage. Moreover very slight alterations are necessary to theswitches and there is no radical departure from the main features ofconstruction and operation which have been proved to give reliableservice.

According to one feature of the invention,

' a plurality of means of access are provided to one or more groups ofsubscribers" lines, the switch or switches affording each means ofaccess being subjected to a different directive control. Thisarrangement may be rendered possible because one or more exchanges workare or-o ded with a plurality Some of.

ElZOS access used being dependent upon the value of the exchangeselecting digit or digits dialled, in which case the connection proceedsin the ordinary way, or according to another feature of the invention,means may be provided for discriminating between connections establishedin response to diifercnt digits so as to enable these connectionssubsequently to be resolved in accordance with said different digits.

The objects of the invention may be attained by the use of speciallymodified autoiatic switches which are not effectively operated inresponse to the first digit but in which this first digit is recordedupon relays,

the switch then operating in the usual manner in response to subsequentdigits.

The operation of the relays may be effected tion taken in conjunctionwith the accompanying drawings. It should be understood however that theembodiments described are by way of example only and that considerablemodifications could be made in the circuit details without exceeding thescope of the invention.

The main object of the invention, to permit the use of large groups oftrunks whereby the economy always associated with large groups can beattained, is achieved by two methods either or both of which may beemployed as desired, firstly, by special slight though importantmodifications of the standard switches which are known to oper atereliably and secondly, by the application of the principle of gradingwhich will be more fully described hereafter.

Referring now to the drawings, Figs. 1 to 9 and 18 are layout diagramsshowing schematically various proposed arrangements of the switches insystems of different Figures 10., 11, 12, 13, 1e, 16 and 17 are de' {DZglut diagrams n e the invention, while Fig. 15 indicates a singlecontact bank showing how the connections are made when gracing isresorted to.

In each of Figs. 1 to 9, and 18 it is assumed that a connection is setup from the subscriber A over the primaryline switchC to the subscriberA having a similar line switch C Dealing first with Fig. 1, thisrepresents the switching plan of a10,000 line exchange in which all theswitches are of the so-called large capacity type, having. two sets ofwipers and corresponding banks and thus having access to 200 lines. Boththe first and second selectors are arranged for simultaneous hunting,but whilethe second selector E has 10 groups each of 20 lines outgoingfrom it, the first selector ,D comprises only 5 gronpseach o't' linessince the two banks oileach switch are multipled together in a specialmanner. This multipling may conveniently be between levels 1.t0 5 in thelower bank and levels (3 to 0 respectively in the upper bank, orbetweenlevels 6 to 0 in thelowerbank and levels 1 to 5 respectively in theupper bank, but other arrai'igements may equally well be employed. Inthe above case it the subscriber dials either 1 or Ghe obtains access tothe same group of 20 trunks; consequently it is necessary to providesome means of discriminat on between the digits 1 and 6, as in generalthey will be required to produce a different final effect.

"Thisdiscrimination is effected by connecting a special potentialmomentarily to one of the speaking leads before the succeeding series ofimpulses, and. this potential is re peated through the second selectorand operto detcrminoiwhich set of wipers of the connector H shall beused. lVith the arrangement shown in Fig. 1 the benefit of large groupsor? trunks is obtained in both the first and second selecting stages,s': co the second selectors are of the 10-level Ell-trunk type andexceptfor the provision for repeating the discriminating potential areidentical with those described in BritishPatent No. 170,385 granted Oct.19, 1921. It may be preferable however in some cases to use. see- 0ndselectors of standard type having groups of ten lines; the desirabilityin any particularinstance will be determined by the specialcircumstances. of the case. Detailed circuit diagrams corresponding toare given in Figs. 10, 11 and 12.

The arrangement. shown. in Fig. 2 is very sim lar except that in thiscase the first selector D is standard and the combination into largegroups takes place at the second selector E which isnow similar to thefirst selector 1) shown in 1. The. connector H again has two sets ofwipers, one or other oi": which is selected in response to the receiptor non-receipt of the discriminating potential, which in this case istransmitted direct from the second selector E Fig. 3 shows anarrangement again applied to a 10,000 line exchange, and very similar toFig. 1. The first selector D in this case is identical with that shownat D .inFig. 1,]ont the second selector-F instead of .a standard switch,or he ngarranged tor. simultaneous hunting overl th banks as in Fig. 1,responds to the discriminating potential to select one or other of itstwo sets of wipers, and connect ons are then made from enact. thetwohanks to separate groups granted F eb. 26, l-920 in which the wipersare only operated by the odd impulses, while the even impulses perform aswitching oper ation. In the specification mentioned it 'will beremembered, the switch had two banks and sets of wipers, the secondset-be-' ing brought into use if an even number of impulses was receivedand the switch was adapted to respond to as many as 20 impulses. Asapplied to the present invention however the switch would only respondto ten impulses and would thus take a maximum of 5 steps. Accordinglythe two sets of wipers will be in parallel and spaced five steps apartrand arrangements will be provided for simultaneoushunting. 'The bankwiring will be such that leyels 1 and 6 lead in the same direction,levels 2 and 7 lead in. the same different direction and similarlylevels 3 and 8 and so on. In order to obtain the required discriminationin this case, the odd impulses are arranged to produce the actualmovement of the switch wipers as before while the even" impulses operatea relay which controls the con nection of discriminating potential ovcrthe line at the righttime in the manner previously descr bed. .Secondselector E is standard except for means for repeating the Ydiscriminating potential and connec'torlFP issimilar to connectors H andH It will be apparent that any of the arrangements shown in Figs. 1 to 1may be applied to a 1000 line exchange with suitable modifications, i.e. in general the elimination of the second selectors so that thediscrimlnating potential is transmitted direct -from the "first selectorto the connector.

Inthe case of a 5,000 line exchange, the ordinary numbering schemeaIi(l"'standaI'(l bank wiring is used something like half the bank iswasted owing tothe first digit being only oneof a possible five numbers.The

systemof bank wiring for the first selector shown'in 4, mayadvantageously he used to attain greater economy in, this case,

messiah being then'of the type shown in Fig. 10 with two sets of wipersspaced five steps apart and a'ranged for simultaneous hunting. Since inthis instance, there is no combination of two different digits, it isunnecessary to send any discriminating potential and the secondselectors and connectors may be or" the standard type, or standard largecapacity second selectors may be employed as in Fig. 1.

Figure 5 shows an arrangement suitable for a i000 line exchange and itsuse enables the first selectors normally used to be eliminated entirely.This is attained by arranging the first selectors such as F to respondto the first series of impulses to register the digit dialled anl thento be operated in the usual manner response to the second digit. Theregistering of the first digit may be effected either by causing theswitch to step up, maize a suitable record and then drop back as in theswitch shown in Fig. 18 or b allowing the first series of impulsesreceived to operate relays direct as in the switch shown in Fig. l i. inorder to secure the necessary discrimination, the selectors such as F,and connectors as H will each have two sets of wipers and according tothe first digit dialled appropriate selection is made between thevarious sets of wipers,there being clearly tour choices available.

Figure 6 shows a similar principle applied to a 400-line exchange, inwhich case obviously one switch such as the connector H impulses, inwhich case a connector shown.

in 17 operating on the principle shown by the selector in Fig. 14: maybe used.

The application of the same principle to a 2,000 line exchange followsat once and is depicted in Figs. 7 and 8. In F igure 7 the firstselector F "is set in accordance with the first digit and afterresponding to the second digit sends a discriminating potential to theconnector H to determine which set of wipers is to be used. In Fig. 8the first digit is employed to determine which set of wipers of the nrstselector F shall be used and two separate groups of connectors such as Hand H may then be employed each of stand ard type.

Figure 9 is concerned with a network in which there are only a smallnumber of exchanges, say less than ten. In this case instead of only onelevel of the bank of the first selector G being allotted to eachexchange as has been usual practice hitherto, each exchange of such sizeas to warrant it is llotted two or, perhaps three levels and by thismeans a large group of trunks may be obtained and the usual savingincidental thereto gained. The second selector E and connector H may nowbe standard in all respects. The combination of two or more levels toform a large group of trunks is effected by applying the principle orgrading, for instance, as indicated in Fig. 15.

Suppose for instance that from the switch of which a single bani: isshown in 15, one rather larger exchange is accessible over levels 2, 3and l and a somewhat smaller exchange over levels 6 and 8, while theremaining exchanges in the network are each acces sible over one levelonly. It may not, however, be desirable to proi ide the full trunks tolead to the medium sized exchange and in this event the first tourcontacts, say, in each of levels 6 and 8 may be individual while theremaining six contacts in each level are multipled together, so that atotal of A trunks is then provided. Similarly in the case oi the largerexchange it is assumed that 20 trunks will be suflicient and hence thefirst 5 contacts in each of levels 2, 3 and 4 are individual, while theremaining 5 in the 3 levels are multipled together so that a total of 20is obtained.

This arrangement of grading may also be employed with advantage in anumber of the cases mentioned above, notably, in the systems shown inFigs. 1, 2 and 3, in fact in allcases in which simultaneous huntingtakes place with discriminating means provided. In Fig. l the firstselector may then be of standard type, with grading betweencorresponding levels such as l and 6, 2 and 7, 3 and 8, and so on. Thisarrangement will also apply to the similar switches shown in Figs. 2 and3. Under these circumstances the trunk lines from individual contactswill extend to ordinary selectors which will he in two different groupscorresponding to the two different portions of the bank. Only the trunksassociated with the contacts which are multipled between a number oflevels need then lead to the modii' ed second selectors and connectorsshown in Figs. 1, 2 and 3. By this means a substantial proportion of theadvantages of simultaneous hunting may be obtained without thedisadvantages or additional wipers and increased complexity; all that isnecessary is to employ a special arrangement of bani: wiring.

A'specially advantageous arrangement on these lines is possible in thecase of a 10.000 line exchange in which the st um bers are distributedsubstantially unirormly from 1000 to 9,999. In this case it is an rangedthat these number which have the first digit even also have the lastdigit even andthose that have the first digit odd have the last digiuodd also, or vice versa. Grading may then be applied to the pairs 01"levels throughout the first selector bank and since 10 discrimination isnecessary succeeding swi hes as wellaas the first selectors may be ofsta dard type.

An alternative construction for these switches whenugrading is notemployed but simultaneous hunting is, 1S toprovide only one bank as inthe ordinary course, but three sets of wipers soaced five steps apart.The upper and lower of wipers .are then. multipled together toform oneset while. the middle wipers form the other set. It will obviously benecessary inthis case to provide sittlicient clearance above and belowand between the banks and the resulting increase in the overall heightof the switch may in some cases be a disadvantage. This construction isdiagrammatically illustrated inl ig. 18.

The general princigles involved and the improved trlmlting schemeincorporating them having been described, a detailed delit = upper bank.with post springs which are operated on halt per bank and the levels 6-0in the lower bank are multipled to levels 1-5 in the The switch is alsoprovlded the number of levels i. e. 5, although it is immaterial whetherthey are operated on five consecutive levels or otherwise, for instanceon alternate levels. The circuits of this switch as wel as that shown inFig. 11 are very similar to those disclosed in British Patent No.170,385, previously referred to, it being arranged that simultaneoushunting takes place over both banks and that the connection is thenestablished with the first idle line encountered by either set ofwipers.

The selector in Figure 11 is also arranged :tor simultaneous hunting butin this case there is no mnltiphng between the banks so that access isobtained to a dili'e'rent group of 20 trunks on each level. Furthermorethe switch is not provided with post. springs but has means forrepeating the discriminatf ing potential which may be momentarilyconnected to one of the speaking leads from the first selector.

Figure 12shows a connector adapted to be used with either of theswitches shown in Figures 10 and 11 and this .is also provided with twobanks and two sets Oil wipers. In tiis case the selection of the bank tohe used determined by the .receiptor.nonsreee ipt of the discriminatingpotential referred to-in connection with Figure 11.

It is assumedthat a subscriber has access to the switch shown in Fig. 10overa primary andpossibly a secondary line switch in the usualway. Vhenthe speaking leads are switched through at the line switch, a circuitcompleted over the loop and conductors 1 and 2 for the line relay .4,which thereupon operates .andv at armature 5 and its front contactcompletes a circuit for release relay 6 from earth at armature and itsback contact, andarinature 11 andits .baclccontact. Relay 6 uponenergizing at armature 7 prepares the impnlsing circuit, armature 8connects earth to release trunk conductor 3 and at armature .9 preparesthe discriminating potential circuit. The subscriber will now proceed todial the first digit in the required number whereupon a number ofinterruptions will be produced in his loop and line relay 4 will.deenergize momentarily a corresponding number of times. On eachdeenergization of the relay't a circuit is completed as follows: earth,armature 10 and its back contact, armature 11 and its back contact,armature 5 and its back contact, armature 7 and its front contact,winding of series relay 14, winding .of vertical magnet 15 to battery.The vertical magnet is thus operated to raise the switch wipers a numberof steps corresponding .to the digit dialled and series-relay. 14 isenergized and being slow'to release remains energized throughout theseries of impulses. At armature 1.6 the following circuit is completedfor the shunt field relay 19 as soon as the switch steps ofi'normal andthe ofi normal springs 17 and 23 are closed; earth, battery, interruptercontact 24, off normal contact 23, left hand winding of relay 19,armature 16 and its front contact and parallel. thereto through theright hand winding. of relay 19 and normally open contact controlled byarmature .16, off normal springs 17, armature 8 and its front contact toearth.

The .shunt field relay 19 is thus energized over bothits wmdmgs andconsequently 0peratos; at .armatures 20 and 21 completes a lockingcircuit for itselt and at armature .22 prepares a circuitfor the rotarymagnet 25. At the endof the train of impulses,

series relay 14: deenergiizes andreleases the armature 16 whereupon acircuit is completed from earth, front contact andarmature 8, off normalsprings 17 normally closed contacts controlled by armature 16, armature22 and its front contact, rotary magnet 25 to battery. The rotary magnetthereupon operates to rotate the wipers one step into engagement withthe first set of bank contacts, at the'samc time opening its interruptercontact 24 whereby the circuit of the shunt field relay 19 is opened.

.Assume for convenience of description that both the sets of wipers arenow in engagement with busy lines so that both wipers 39 and will findearth. In these cireumstances a circuit may be traced from wiper 39,armature 30 and its back contact, right hand winding of relay 19, offnormal contact 2, interrupter contact 24 to battery, and a similarcircuit from wiper 40, armature 28 and its back contact, left handwinding of relay 19 to battery by way of contacts 23 and 24- as before.In these circumstances relay 19 again energizes and the rotary magnet isagain connected up over the circuit previously traced and the switchmoves another step.

Suppose now that only wiper 39 finds earth on the contact with which itis now in engagement. Since relay 19 only operates its armature whenboth its windings are energized it will not now do so but a circuit maybe traced as follows: battery, interrupter contact 24:, off normalcontact 23, left hand winding of relay l9, winding of relay 26, armature31 and its back contact, off normal contact 17, armature 8 and its frontcontact, earth. Relay 26 operates in this circuit, at its armature 29opens a point in the circuit of relay 27, at its armature 10 opens apoint in the circuit of the release magnet, at armature 28 connects therelease trunk conductor through to wiper l0 and at armatures 34 and 35disconnects line relay i and connects the speaking leads through to theline wipers 43 and 4.4.

It should be mentioned that to provide for the case in which both thetest wipers encounter free trunks at the same instant, the adjustment ofthe relays 26 and 27 is so arranged that one, say relay 26, will alwayspull up slightly before the other and thus open its circuit at armature29. It should also be mentioned, that the springs 17 and 18 are not offnormal springs of the ordinary type operated by the switch shaft, butare closed when the vertical magnet energizes and opened when therelease magnet energizes.- This provision is made to obviate thepossibility of relay 19 energizing and locking up in case both testwipers should encounter busy trunks simultaneously during the releasemotion.

Suppose that in the present instance the post springs 38 have beenoperated: in this case on the operation of relay 26, earth is connectedto the lower speaking conductor and wiper A by way of post springs 38,

armature 9 and its front contact, front contact and armature 32,armature 35 and its front contact. t will be seen that this connectionis only momentary since it will be removed as soon as relay 6 releasesand opens armature 9.

As soon as relay 26 switches through, a circuit is completed for relay45 of the second selector Fig. 1l as follows: battery,

as before.

upper winding of relay lf), back contact and armature 58, back contactand armature 52, contact with which the wiper 43 is in engagement andsaid wiper, front contact and armature 34, lead 1, over subscribeflsloop,

the lower winding of relay 19, at armature 69 prepares the impulsingcircuit and opens a point in the circuit of the release magnet .73 andat armature 7O prepares a circuit for repeating the discriminatingpotential to the succeeding switch. It will be observed that owing tothe connection of earth to thelower trunk conductor, relay 49 is shortcircuited and hence does not operate. In response to the dialling of thenext series of impulses, vertical magnet 7 2 is operated to step thewipers to the proper level. Series relay 4''? is operated throughout theseries of impulses and at its armature 71 completes the circuit for theshunt field relay 48 as soon as the off normal contacts 7% close. Whenthe normally closed springs controlled by armature 71 are again closed acircuit is completed by way of armature 7 8 and its front contact forrotary magnet 79 and the hunting movement takes place lVhen a free lineis encountered by either wiper 82 or wiper 83, one or other of relays 50and 51 will operate.

Suppose in the present case that relay 51 operates; at its armature 59it connects release trunk conductor 8% through to test wiper 82, at itsarmature 60 opens the circuit of the releasemagnet Q 3 extending overthe off normal contacts 75 which are now closed, at its armature 61opens a point in the circuit of relay 50, at armature 62 connects up thediscriminating potential to the lower speaking conductor and atarmatures 58 and 63 disconnects line relay 45 and connects the speakingleads through to wipers 76 and 77.

When this occurs a circuit completed for the line relay of the connectorin Fig. 12 (which is assumed to be seized over wipers 76, 77 and 82) asfollows: battery, upper winding'of relay 86, contact on which wiper 76is resting and said wiper, upper speaking lead, front contact andarmature 58, back contact and armature over the subscribe'rs loop,armature 62 and its front contact, armature and its back contact,armature and its front contact to earth. Relay 86 energizes inv thiscircuit and at its armature 87 completes a circuit for release relay 88which energizes also. Relay 88 .70 lead 2, armature 32 and its frontcontact,

upon operating, at armature 89 connects earth to the release trunkconductor 85, at armature 90 prepares the testing circuit, at armature91 connects up the lower winding of relay 86 at the same timedisconnecting the lower winding of relay 118 and at armature 92 preparesthe impulsing circuit.

When the subscriber dials the next digit, relay 86 is de-energized acorresponding number of times and on its first de-energizati'oncompletes the following circuit: earth, armature 8'7 and its backcontact, armature 92 and its front contact, spring 94 and spring 95 withwhich it is normally in engagement, winding of series relay 93, verticalmagnet 98 to battery. The series relay is energized in this circuit andat its armature 97 serves to maintain its own circuit and that of thevertical magnet intact when the off normal springs shift as occurs onthe first step of the switch.

At the end of the train of impulses, re-

lay 93 de-energiz'es and releases armature 97 so that on receipt of thefollowing train of impulses, a circuit is completed for the rotarymagnet 102 as follows: earth, armature 87 and its back contact, armature92 and its front contact, off normal springs 92k and 96, armature 97 andits back contact, back contact and armature 105, armature 109 and itsback contact, rotary magnet 102 to battery. A branch of this circuitextends through the winding of relay 99, which being slow to release,remains energized throughout the train of impulses. Relay 99 at armature101 connects the busy relay 103 by Way of armature 120 and its restingcontact to test wiper 125 and at its armature shunts armature 105 sothat the circuit of the rotary magnet is not interrupted in case thebusy relay 103 operates during the rotary movement. This will happen ifwiper 125 should pass over busy lines whereupon relay 103 in addition tooperating armature 105 will at its armature 104- prepare a lockingcircuit for itself. If the called line is busy, relay 103' will beenergized when the switch comes to rest and upon the de-energization ofrelay 99 will be locked up in the circuit; earth, armature 90 and itsfront contact, armature 104 and its front contact, normally closedsprings controlled by armature 101, winding of relay 103 to battery. Inthis case the operation of arma ture 116 will connect busy tone to theline so that the calling subscriber is notified and hangs up hisreceiver thereby releasing the connection. It will be assumed howeverthat the called line is idle hence relay 108 will not be energized whenrelay 99 de energizes and instead the following circuit will becompleted when armature 101 engages with its back contact: earth,armature 90 and its front contact, armature 10 1 and its back contact,upper winding of relay 106,

back contact and armature 101, armature 120 and its back contact, wiper125, cut oil relay and driving magnet associated with the calledsubscribers line switch to battery.

The cut oil relay operates in this circuit to clear the line of itsnormal battery and earth connections and relay 106 also operates, atarmature 108 completes a locking circuit for itself to the release trunkconductor, at armature 109 opens the circuit of the rotary magnet sothat any further impulses' which may be sent will be ineffective, atarmature 107 places direct earth on test wiper 12a and at arn'iatures110 and 111 connects the ringing generator RG and the upper winding ofringing trip relay 112 respectively to the subscribers line so that heis rung in the usual manner. Vhen he replies relay 112 is operated bydirect current over hisloop, at its armature 113 com-' pletes a lockingcircuit for itself and at armatures 114 and 115 disconnects ringingcurrent and completes the speaking leads. The back bridge relay 117 isnow energized and operates at armatures 130, 131 to reverse the currentflow over the calling subscribers line for metering or like purposes.The subscribers may now converse and at the end of the conversation theconnection is released when the calling subscriber hangs It may bedesirable at this oint to explain the sequence of operations in case thepost sirings 88 in Fig. 10 are not operated. In this case when relay 26switches through, the lower winding of relay 19 which was previouslyshort circuited is now operative so that the relay energizes and atarmature 64:

completes a locking circuit for itself to release trunk conductor S land at armature 65 opens the circuit for repeating the discriminatingpotential to the succeeding switch. Similarly when relay 51 switchesthrough, owing to the absence of discriminating potential. on the lowertrunk conductor, relay 118 is operated over its lower winding and atarmature 119 completes a locking circuit for itself and at armature 121,120 and 122 disconnects the normal set of wipers and connect-s up thesecond set. It will thus be seen that outgoing from the first selectorthere were five groups of twenty trunks instead of the usual ten groupsof ten trun {S with which arrangen'ient an appreciable saving of secondselectors is possible, and that the combination which took place at thefirst selector is resolved at the connector by means of the dis--criminating potential which is repeated over the second selector.

Referring now to Figure 13 this indicates a circuitof a selectorsuitable for use in a layout such as that indicated. in Figure 5, i. e.the case of a 4,000 line exchange. Accord.- ing to this arrangement uponreceipt of the first digit the switch is operated in the usual mannerbut is then immediately released whereupon it is enabled to respond to afurther digit, after which an automatic hunting operation takes place.In response to the first movement, however, suitable post springs areoperated so as to energize either or both or neither of two relays,bywhich means the first digit, it one of a possible four, can be recorded.This switch also has two sets of wipers one or other of which is usedaccordin; to the operation or non-operation of one of the said relays,while the other relay controls the connection of a momentarydiscriminating potential to the line. The operations involved will nowbe described in detail. I

1V hen the switch is taken into use, for instance in known manner overan individual line switch associated with a subscribers line, thefollowing circuit is completed: bat tery, upper winding oi line relayback contact and armature 236, conductor 201, over the subscribens loop,conductor 202, armature 23S and its. back contact, lower 'inding ofrelay 20% to earth. Relay 201 operates and at its armature 205 completesa circuit for the release relay 206. Relay 206 upon operating, atarmature 207 connectsearth to release trunk conductor 203 and prepares aholding circuit for relay 214i and at armature 208 prepares theimpulsing circuit. When the subscriber dials the first digit, the relay204 is deenergized a number of times and at each deenergization thefollowing circuit is completed: earth, armature 205 and its bac;contact, armature 208 and its front contact, winding of series relay209,vertical magnet 211 to battery. The switch is thus raised to the levelcorresponding to the digit dialled and the series relay 209 being slowto release remains energized throughout the train or" impulses. Supposefor the sake of example, that the digit 1 has been dialled and that onthe fourth level both the post springs 215 and 218 are operated.

Accordingly when relay 209 deenergizes a circuit is completed from earthon armature 207 and its front contact, armature 210 and its backcontact, armature 225 and its back contact, post springs 215, normallyclosed contacts controlled by armature 216, winding of relay 21 1 tobattery and parallel thereto, post springs 218, normally closed springscontrolled by armature 22,0, winding of relay 219 to battery. Relay 214upon operating, at armature 216 completes a locking circuit for itselfdependent upon armature 207 and at armature 217 prepares the connectionof the discriminating potential to the lower trunk conductor. Relay 219upon operating at armature 220 completes a locking circuit for itselfand at armature 221, 222 and 223 disconnects the first set of wipers andconnects up the second set.

A circuit is also completed on the doomergization of relay 209 whichextends from earth on armature 207, armature 210 and its back contact,oil normal springs 212, armature 228 and its back contact, releasemagnet 213 to battery. A branch of this circuit also extends by way ofthe normally closed springs controlled by armature to the winding ofrelay 224. The release magnet therefore operates in this circuit torestore the switch to normal, and relay 22a is encrgized. Upon operatingat its armature 225 it opens a point in the circuit for relays 21% and219, so that if these have not been already operated they cannot beoperated on the succeeding vertical movement of the switch, at armature226 locks itself up to release trunk conductor 203, at armature 228opens its circuit for the release magnet and at armature 227 prepares acircuit for the stepping relay 231. The switch is thus re leased afterrespon d'ng to one digitwhatever the value of that digit.

The subscriber will now proceed to dial the next digit, whereupon thenumber of interruptions are again produced in the circult of line relay201 and it deenergizes accordingly. Upon each de-energizatiou a circuitis completed as previously traced and the vertical magnet 211 of theswitch is stepped up to the corresponding level. As soon as the oilnormal contacts 229 close, a circuitis completed from earth on releasetrunk conductor 203, armatnre 210 and its front contact, interruptercontact 230, off normal contacts 229, armature 227 and its frontcontact, winding of stepping relay 231 to battery. Relay 231 at armature233 prepares a circuit for the rotary magnet 23 1 and at armature 232completes a locking circuit for itself dependent upon the interruptercontact 230 of the, rotary magnet, At the end of the train of impulseswhen relay 209 releases, a circuit is completed from earth on releasetrunk 203, armature 210 and its back contact, front contact and armature233, winding of rotary magnet 23% to battery. The switch wipers are thusmoved one step into engagement with the first set of contacts. Theoperation of the rotary magnet 23-1C opens nterrupter contact 230 sothat stepping relay 231 is deenergized. If test wiper 240 finds earth onthe contact with which it is in engagement, a circuit for relay 231 willbe again completed and it will energize thereby closing contact 233 andcausing; rotary magnet 23 1 to advance the switch wipers turther step.This operation continues until the test wiper 2 10 engages a contactwhich is not earthed, whereupon switching relay is no longer short circuted and energizes in the follow ing circuit: battery, winding of relay231, front contact and armature 227. oil normal contacts 229,interrupter contact 230, winding of relay 235 to earth on release trunkconduct-or 203. Stepping relay 231 is not energized in this circuitowing to the high resistance of relay 235. This latter relay, however,operates and at armature 237 connects release trunk conductor 203 totest wiper 240, at armatures 236 and 238 connects the speaking leadsthrough and disconnects the line relay -1 and at armature 239 connectsdiscriminating earth on armature 217 to the lower trunk conductor 202.lVhen relay 20d deencrgiZes the circuit of relay 206 is opened and itdeenergizes also thereupon releasing its armature 207 so that thecircuit of relay 21-1 is opened; the connection of earth to lowcr trunkconductor by way of armature 217 i s thus only momentary. Thisconnection of earth may operate a connector such as is shown in Fig. 12in the same manner as was described in connection with this figure, andthe connection is completed in a manner which will be readily ajzpreciated from the description already given of Fig. 12.

The circuits of a switch 01 a similar kind are illustrated in Fig. 14,this switch however being arranged so that its wipers are not moved inresponse to the first d git as in the case of the switch in Fig. 1.3,but instead the number received is'set up on relays d rect. As before itwill be assumed that the first digit transmitted to this switch is four.\Vhen the switch is taken into use, for instance over the subscribersline switch, a circuit is completed over the subscribers loop andarmatures 3 10 and 344- and their back contacts for the line relay 300.This relay upon operat ng completes a circuit for the release relay 302,which at armature 303 connects earth to release trunk conductor 299 andat armature 1 prepares a locking circuit for relay 333. Relay 302moreover at armature 305 prepares the impulsing circuit and at armature306 prepares a circuit for transmitting a discriminating potential v tothe next switch it necessary.

The subscriber now dials the digit 4 and in response to the firstinterruption in the loop, relay 300 is deenergi ed and a circuit is thencompleted from earth, back contact and armature 3 12, armature 301 andits back contact, armature 305 and its front contact, winding of relay309, armature 337 and its back contact, armature 321 and its backcontact, lower winding of relay 319 to battery. It should be mentionedat this point that the relays 319, 325 and 333 are each of the twostepvariety arranged to operate a light armature when current traversestheir lower windings only and to operate all their armatures when theyare energized Over both windings in series. In response to the firstimpulse therefore, relay 319 operates only its armature 320 wherebyearth is connected to the other terminal of its upper winding over backcontact and armature 335 and back contact and armature 329. hen

armature 301 leaves its back contact on the termination of the impulse,the upper winding of relay 319 is no longer short circuited and therelay operates fully, thereby at armature 321 transferring the impulselead to relay 325 by way of armature 328, at

armature 322 preparing a locking circuit for relay 333 and at armatures323, 324. and 325 disconnecting the normal set of wipers and connectingup the second set. Relay 309 is energized in the impulsing circuit andbeing slow to release, remains energized throughoutthe train ofimpulses; at armamature 310 it opens a point in the circuit of therotary magnet 313, at armature 311 prepares a circuit for the steppingrelay 314, which circuit is, however, inellective during this train ofimpulses since the offnormal contacts 318 do not close, and at armature312 opens a point in the locking circuit of relay 333.

\Vhen relay 300 next deenergizes the impulsing circuit extends aspreviously traced to armature 321 and thence over its front contact andarmature 328 and its back contact through the lower Winding of relay tobattery. Relay 325 operates its light armature 327 at this time and onthe termination of the series of impulses operates fully; thereupon atarmature 331, another point is closed in the circuit for connecting updiscriminating potential, at; armature 329 the locking circuit of relay319 is opened so that it deenergizes, at armature 328 the impulsingcircuit is transferred to relay 333, and at armature 330 another pointis prepared in the circuit of relay 333. The succeeding impulse extendsover the same circuitas did the first since relay 319 is now deenergizedagain; for this reason no circuit is now completed for relay 333 sincearmature 321 has released. Relay 319 therefore operates all itsarmatures with the same results as before, its locking circuit nowextending over the front contact of armature 329; thus both relays 319and 325 are now energized. Upon the succeeding deenergization of relay300 it again completes the impulsing circuit which now extends overarmature 321 and its front contact, armature 328 and its front contactlower winding of relay 333 to battery. This relay at once operates itslight armature 33-1 and on the termination of the impulse operates allits armatures; thereupon at armature 335 the locking circuit of relays319 and 325 is n1omentarily opened, so that they both deencrgize, and atarmature 337 the impulsing lead is transferred to the vertical magnet338. The final result therefore with a train of four impulses is thatrelay 333 only is operated and is held locked up to earth on arma ture304. Hence the normal set of wipers of the first selector will be usedand since no discriminating potential will be sent over the line, thenormal set of wipers of the connector also will be used.

Upon the dialling of the succeeding digit the impulsing circuit asexplained now extends to the Tertiral magnet and consequently the switchshaft and wipers are raised a number of steps corresponding to the digitdialled. The circuit for the stepping relay 314 is completed as soon asthe off-normal contacts 318 close and upon the release of relay 309 theswitchcommences to hunt in known manner. \Vhen it finds a free line,relay 339 is operated and disconnects the line relay and switchesthrough the speeding leads at armatures 340 and 344 and at armature 343closes another point in the circuit for connecting discriminatingpotential to the lower trunk conductor.

As mentioned above in the case in question since neither of the relays319 or 325 remains operated, the first or normal set of wipers is usedand no discriminating poten-. tial is sent out to the next switch. Incase hon-ever, the first digit dialled is 1 instead of 4, relay 319would be energized as before and relay 309 would then deenergize sinceno further impulses are being sent. When this occurs a locking circuitfor relay 319, is closed over an alternative path by way of back contactand armature 311 and a circuit is also completed from earth, armature312 and its front contact, armature 322 and its front contact, bothwindings of relay 333 to battery. Relay 333 therefore at once operatesall its armatures with the results previously described except thatsince the circuit of relay 319 is now maintained intact over armature311, relay 319 remains energized. When the succeeding impulses are sentfor operating the vertical magnet relay 319 is *iaintained energizedover the front contact 335 of relay 333 during the operating of rela309.

If a train of two impulses had been sent relay 319 would first have beenenergized and then relay 325, relay 319 being deenergized by theoperation of relay 325. On the ibsequent deenergization of relay 309 acircuit would have been completed for relay as before and in this caseclearly the final result is the energizationof relay 325 so that thefirst set of wipers would have been. used and no discriminatingpotential would have been sent.

Should the first digit be 3, both relays 319 and will be energized andin this case since their locking circuits are completed at armature 311and its backcontact before armature 335 is operated they both remainenergized. In this case therefore, the second set of wipers is used anddiscriminating potential is sent out to the next switch, Thisdiscriminating potential (earth) is connected up when the switchingrelay 339 operates and extends over front contact and armature 343,armature 306 and its front contact, front contact and armature 331 tothe lower speaking lead. Since the circuit of the line relay 300 isopened when relay operates and this then opens the circuit of therelease relay 302, the connection of earth to the lower trunk conductoris only momentary. The arrangements for responding to it can be similarto those provided for responding to the similar operation in the case ofthe switch shown in Figure 10, i. e. a connector of the type shown inFigure 12. Thus the switch shown in Figure 14 as well as that shown inFig. 13 is adapted to respond to the first digit received by in withoutany effective movement of its wipers, the said first digit however beingarranged to selectively determine the ultimate destination of thecall.

Refer now to Figure 17 in which is shown the circuit of a connectorsuitable for use in a layout such as that indicated in Figure 6, i. e.the case of a 400 line exchange. According to this arrangement uponreceipt of the first digit the switch is operated in the usual manner,but is then immediately released whereupon it is enabled to respond totwo more digits. In response to the first movement, however, suitablepost springs are operated so as to energize either or both or neither oftwo relays, by which means the first di 'it, if one of a possible four,can cause tne wiper set having access to subscribers of the desiredhundred .to be connected for use. Since the principle of selectingwipers is the same as that shown in Fig. 13 a detailed description ofoperation is thought unnecessary.

The circuits of a switch of a similar kind are illustrated in Fig. 16,this switch however, being arranged so that its wipers are not moved inresponse to the first digit as in the case of the switch in Fig. 17, butinstead the number received is set up on relays direct. This switch usesthe same principle of selecting wipers as the selector shown in Fig. 14and in view of the previous description a detailed description istherefore thought unnecessary.

It should be mentioned that though in all the examples described withthe exception of the arrangement shown in Fig, 9, a local connection hasbeen assumed i. e. one entirely within a single exchange, it must not beas sumed that the improved trunking schemes are limited to sucharrangements. On the contrary, the invention may also be applied totrunking between exchanges or standard trunking may be used betweenexchanges and the improved arrangements for the local portion only. Incase repeaters should be required for inter-exchange working, these canbe arranged to repeat the discriminating potential by the provision inthe second selector in Fig. 11 or the connector in Fig. .12.

It should also be mentioned that though connections have been describedasextended direct from a calling subscriber, the im proved switches willclearly work equally well in response to impulses sent from a registertranslator; probably in this case, however, it would be preferable touse standard switches and effect the necessary changes in the registertranslator.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be per formed, we declarethat what we claim. is:

1. In an automatic telephone system a switch train responsive to thedigits of a call number to extend a connection, a plurality of wipersets on the last switch of said train and means controlled by the firstof said digits forcontrolling the application or non-applicationof adiscriminating poten: tial to said last switch for determining the wiperset to be used by said last switch.

2. In an automatic telephone system, a switch train responsive to thedigits of a call number to extend a connection, a plurality-of wipersetson the last switch of said train,-and means in the first 01. saidswitches controlling the application or non application of a potentialto said last switch for determining'the wiper set to be ,used by saidlast switch.

3.; In an automatic telephone system, a switch train responsive to thedigits, of a call'number to extend a connection, a plurality of wipersets on the last switch of said train, means in the first of saidswitches responsive to the first of said digits for directivelyoperatingsaid switch and means also in 'the first. said switch and controlled bysaid directive operation for controlling the application ornon-application of a potentialfto said last switch for determining thewiper set togbe used by said last switch.

4. In an automatic telephone, system, a switch train comprising a switchresponsive to the first, a switch responsive to the second, and aswitchresponsivc to the last two digits of a call number to extend aconnection, a plurality of wiper sets on the last said switch, meansin-said second switch for selecting the wiper set to be usedby said lastswitch and means in said first :switclnfor controlling said selectingmeans,

5. In arr-automatic telephone system, a switch train comprising a switchresponsive to the first, a switch responsive to the second, and a switchresponsive to the last two digits of a-call number to extend aconnectioma plurality of wiper sets on the last'said switch, a relay insaid second switch arranged to apply a discriminating potential-to said"last switch to select the wiper set to be used, and means in said firstswitch for controlling-saidrelay.-

6. In an automatic telephone system, a a switch train comprising aswitch responsive to the first, a switchresponsive to the sec.- ond, anda switch responsive to the last two digits of a call number to extend acon nection,-a plurality of wiper sets on the last saidswitch; means insaid second switch for 1 tion,..a plurality of :wiper sets on the last 7said switch, a relay. in second switch arranged to apply adiscriminating potential tosaid last switch to select the wiper set tobe .used, .anda shaft operated spring set in said first switch forcontrolling said .relay.

8. In an automatic telephone system, a plurality Oil serially relatedswitches used in establishing a connection, the first of said switchesbeing accessibleiover a plurality of trunk routes, a plurality of trunkroutes leading front a-scond of said switches, means a for seizing saidfirst switch and operating it into connective relationwith said secondswitch'and means dependent upon the trunk route over which said firstswitch was'seized for determi-ningthe trunk route selection of saidsecond switch.-

9.111 an automatic telephone system, a plurality of serially relateddirective switches used in -extending a talking connection,-a pluralityof wiper sets on -a second oneof said-switches, means for operating offirst of said switches into connective relationwith saidsecond switch,means in saidfirst switch for then sending a directiveimpulse over oneside of said connection to determine the wiper set to be used by saidsecond switch, and means for then directively operating said secondswitch to complete said connection.

10. In an automatic telephone system, a switch train comprising a first,second, and a last switch, a plurality of wiper sets on said lastswitch, a plurality of trunk paths over which said second switch isaccessible. to said first switch in accordancewith first digits ofdifl'erentvalucsand means determined by the path over which said secondswitchiisseized for determiningthe wiper tet to-be used by said lastswitch.

11 In an automatic telephone system, a switch train comprising a first,second, and a lastv switch, a plurality of wipers on said last switch,means for extending a talking connection through said switches, means insaid first switch for momentarily applying a directive potential to oneside of said connection to said second switch, means in said secondswitch responsive thereto to apply a similar potential to one side ofsaid connection to said last switch and means in said last switchcontrolled by said potential to select the wiper set to be used incompleting said connection.

12. In an automatic telephone system, a switch train comprising threeswitches, the second switch accessible to the first over a plurality ofpaths responsive to digits of different values, a plurality of wipersets on said third switch, and means controlled by thevalue of the routeselecting digit re ceived by said first switch for determining the wiperset to be used by said third switch.

13. In an automatic telephone system, a switch train comprising aconnector having a plurality of wiper sets, and intermediate selectorswitches thru which said connector is accessible to a first selectorswitch, said selectors responsive to the digits of a call number forextending a connection to said connector, and means dependent uponwhether the first digit of said series is even or odd for determiningthe wiper set to be used by said connector.

14. In an automatic telephone system, a connector switch having aplurality of wiper sets, a selector switch having access to saidconnector, a shaft on said selector, magnets for operating said shaft, aregister, circuit means for directing the odd impulses of a digit tooperate sazd magnets and the even impulses of said digit to operate saidregister, and means controlled by said register for determining thewiper set to be used by said connector.

15. In an automatic telephone system, a connector switch having aplurality ofwiper sets, a selector switch having access to saidconnector a shaft on said selector, magnets for operating said shaft, aregister, circuit means for directing the odd impulses of a digit tooperate said magnets and the even impulses of said digit to operate saidregister, said magnets operating said switch into connection with saidconnector and means controlled over said connection by said register fordetermining the wiper set to be used by said connector.

16. In an automatic telephone system, a connector switch having aplurality of wiper sets, a selector switch having access to saidconnector, a shaft on said selector, magnets for operating said shaft, aregister, circuit means for directing the odd impulses of a digit tooperate said magnets and the even impulses of said digit to operate saidregister, said magnets operating said switch into connection with saidconnector, said register momentarily applying a selecting potential Illto on side of said connection to select the wiper set to be used by saidconnector.

17. In an automatic telephone system, an automatic switch having accessto second automatic switch, a plurality of wiper sets on said secondswitch, means responsive to a digit received by said first switch foroperating its mechanism, means responsive to said operation forregistering said digit and for returning said mechanism to normal, meansfor then operating said mechanism into connective relation with saidsecond switch and means dependent upon said registering digit fordetermining the wiper set to be used by said second switch.

18. In an automatic telephone system, a plurality of serially relatedautoi'natic switches having a. plurality of wiper sets, means in a firstone of said switches for registering the first digit received thereby todetermine the wiper set to be used by that and a succeeding switch, andmeans l'or sub-- sequently moving the selected wipers of said firstswitch into connection with a second one of said switches.

19. In an automatic telephone system, a switch train comprising switcheshaving a plurality of sets of wipers, a register relay in the first ofsaid switches operated by the first digit received to thereby determinethe wiper set to be used by said first switch, means for operating saidswitch into connection with a second sw h, and means controlled oversaid connection by said relay for determining the wiper set to be usedby said second switch.

20. In an automatictelephone system, a switch train comprising switcheshaving a plurality of sets of wipers, a register relay in the first ofsaid switches responsive to the first digit received thereby todetermine the wiper set to be used by said first switch. means foroperating said switch into connection with a'second switch, said relaycon trolling the application of a directive impulse to one side of saidconnection to select the wiper set to be used by said second switch.

21. In an autoi'nati-c telephone system, a switch train comprisingswitches each having a shaft carrying a plurality of sets of wipers, aregister relay in the first of said switches, shaft operated means forcontrolling said relay, means for operating said shaft into engagementwith said controlling means and for then releasing the shaft, means forsubsequently operating said switch into engagement with a. secondswitch, the switch selected and the wiper set of the second switch to beused being controlled by said register relay.

22. In an automatic telephone system, a selector switch having wipers,means in said switch for registering a digit for a call number withoutmoving said Wipers, means responsive to a subsequent digit for movingsaid wipers .to extend a connection to a second switch, and meanscontrolled by said registered digit to control said second switch.

23. In an automatic telephone system, a. selector switch having wipers,relays in said switch for registering the first digit received therebywithout moving said wipers, and

means responsive to a subsequent digit for moving said wipers to extenda connection to a second switch, and means controlled by said registereddigit to control said second switch.

24. In an automatic telephone system, a selector switch having aplurality or wiper sets, a relay group in said s itch for registeringthe first digit received thereby without moving said wipers, said groupcomprising a relay arranged to select a set of said wipers, and a relayarranged t connect a discrimi nating potential to the line.

25. in an automatic telephone systenna switch having" wipers thru whichother switches are reached, means for re 'isteriug the first digitreceived by said swr h without moving said wiper said registering meanspreparing circuit fo subsequently repeating a special code to t adistinc tive setting of said second itch.

26. In an automatic telephone system a group of selector switchesdivided into a plurality of sub groups, a plurality of trunk linesaccessible to said switches and multiple connections such that certainof said trunk lines are individual to each of said sub groups and otherof said trunk-lines are common to said group of switches, directiveswitches terminating said individual and said common trunks, and meansfor operating said switches through said selector.

2?. in an automatic telephone system, a calling line and a switchaccessible thereto, 1 bank containing a plurality of groups of contactsvassociated with said switch, a plurality oi? wiper 's on said switch,trunk groups leading to said contacts, the number of trunk groups beingless than the number of said contact groups, and multiple connectionsbetween said contact groups such that certain of said trunks areaccessible to said calling line thru di'ii'erent ones of said wiper setsresponsive to two or more values of digits dialled from saidcallingline.

in an automatic telephone system, a switch. train comprising a switchresponsive to the first, (i switch responsive to the second,

and a switch responsive to the last two digits or a call number toextenca connection, a plurality of wi mr sets of said last switch, and 1 msin. said first switch for selecting the wiper set to be used by saidlast switch.

29. in an automatic telephone system, a group of switches divided intotwo subgroups, a plurality of wiper sets on each of said switches, asecond switch having access to said first sw1tches, .a plurality ofwiper sets on said second switch, each of the.

call number to extend a connection, a plu rality of wiper-sets on eachof said switches,

means for operating a first position switch of said train, means in saidswitch for extending a connection to a second position switch cv a wiperset of the first switch end switch, and meansin said first switch--determinin r the wiper set to be used by second switch irrespective ofthe wiper set used by the first switch.

31. In an automatic telephone system, a switch having two sets ofwipers, a group of switches accessible to said first switch throughoneor the other of said two sets of wipers,

means for operating said first switch into connective relation with saidgroup of switches, means in said first switch for simultaneously huntingfor an idle one of said group ofswitehes and for connecting with saididle: one through the wiper set engaging it, a plurality of wipersets'on said second switches and means in said first switch for applyinga discriminating poten tial to said connected second switchirrespectireof the wiper set used by the first switch to determine the wiper set tobe used by said second switch.

32. In an automatic telephone system, a switch train comprising threeserially related switches,- a plurality of wiper sets on each of saidswitches, means for operating the first switch into engageu'ient:withthc second and the secoudinto engagement with the third,automaticmeans, dependent upon trunk conditions for determining thewiper sets to be usedi by said-first and second switches, and means insaid first switch for determining the wiper set to he used by saidthirdswitch irrespective of the wiper sets used by the first and secondswitches.

Signed by me, atLondon, England, this 22nd day of August,192 -l.

RICHARD MERGER.

Signed by me at London, England, this 22nd day of August, "1924. 7 v

FRANK TENCH.

selected by the busy or idlecondition of said

